This invention relates to a thin film device for use in displaying images with a beam of electrons.
There have been recently developed image display devices of the type called a "light valve." Light valves include a layer formed of a dielectric material such as an oil of the paraffin series or a thermoplastic resin and adapted to be irradiated with a beam of electrons making the layer uneven. By putting the layer with the unevenness in an optical system utilizing the schlieren method, an image can be formed with visible light. Alternatively the image may be magnified. When irradiated with a beam of electrons in a vacuum, oils of the paraffin series or thermoplastic resins are decomposed either to evolve gases or to deteriorate the performance of the devices. Thus such light valves have had disadvantages in that the dielectric film involved is always required to be held in a vacuum by using a vacuum pump and the film has a short usable life.
In order to eliminate these disadvantages, there have been already proposed thin film devices of the type including a plurality of strip-shaped electric conductors evaporatively deposited on a glass substrate and a thin metallic film disposed on the substrate through those conductors. According to the principles of light valves employing the thin film device as above described, a beam of light from a source of light falls upon a collimating lens to be formed into a parallel beam of light. Then the parallel beam of light is reflected from the thin film device positioned on a front surface of an evacuated enclosure including therein an electron gun. The beam of light reflected from the thin film device is incident upon a projection lens to be focussed on a stop. However that portion of light reflected from the uneven area of the thin film device forms an image on the associated projection screen, without its passage through the stop.
In addition thin film devices have been previously produced, by way of trial, by filling spaces between strip-shaped electric conductors disposed on the glass substrate with a resin and evaporatively depositing a thin metallic film upon the conductors and resinous portions therebetween. Thereafter the resin has been removed from the device by means of a solvent therefor. In order to remove the resin from the device, it has been required to form openings in the thin metallic film. For example, a construction has been actually produced, by way of trial, including a plurality of strip-shaped electric conductors disposed in spaced parallel relationship on a glass substrate and a thin metallic film in the form of spaced parallel strips connected orthogonally to the electric conductors. In such a construction, it has been difficult to completely remove the resin from between the thin metallic film and the glass substrate. If that thin film device was used in an image display device, that portion of the resin left between the film and substrate could be decomposed upon the irradiation by a beam of electrons, resulting in both the deterioration of the performance and a decrease in the useful life of the device. If the strip-shaped thin metallic film had a decreased width to widen the openings in the metallic film in order to completely remove the resin from the film and substrate, then light would be transmitted through the widened openings with no effect. This does not contribute to the display of images and therefore leads to a loss of brightness of the resulting images that is one of the characteristic features of light valves. Also the strip-shape construction of the thin metallic film decreases the mechanical strength in the lateral direction thereof although no problem occurs in the longitudinal direction thereof. This has resulted in the disadvantages that the thin metallic film easily disengages from the conductors at the junctions there-between and the junctions are easily broken. Only the thin film devices as above described could be produced heretofore.
In order to eliminate these disadvantages, the present applicants have previously proposed a thin film device comprising a substrate formed of a dielectric material having a light transmitting property, a plurality of electrically conducting strips disposed in rows and columns on the dielectric substrate to form a lattice thereon and a thin metallic film having no gap over the entire area thereof and superposed on the conducting lattice with the metallic film fixed at the periphery to the substrate. Since the resulting device has one surface the entire area of which is formed of the thin metallic film, the device can reflect substantially 100% of a quantity of light from the associated source of light falling thereon and be effectively utilized to display images. Thus it serves to produce images with a high brightness. The device does not exhibit the undesirable effect of resin remaining therein because resin is not used to fill the spaces between the conducting strips during the production of the device. Also the device can be used for a long time because the thin metallic film has no gap and excellent mechanical strength.
However, upon producing the device, the thin metallic film preliminarily prepared by an evaporation technique is merely superposed on the conducting strips protruding from the dielectric substrate while being bonded to the substrate at the periphery not bombarded with a beam of electrons. In other words, the thin metallic film is not bonded to the conducting strips. In operation, each square enclosed with the adjacent portions of the conducting strips above the dielectric substrate is projected, as one elementary area of an image, on a projecting screen. In this case, an increase in contrast of the image affects the adjacent portion of the metallic film resulting in a decrease in resolving